Flame‐retardant mechanism of silica: Effects of resin molecular weight

The effects of resin molecular weight on the flame‐retardant mechanism of silica were studied with two different molecular weights of poly(methyl methacrylate) (PMMA), 122,000 and 996,000 g/mol, and two silicas, fused silica with a small surface area and silica gel with a large surface area. A total of six different samples were studied, with a mass fraction of 10% silica. The mass loss rate of the six samples in nitrogen and the heat release rate from burning in air were measured at an external radiant flux of 40 kW/m². The addition of silica gel to the low‐molecular‐weight PMMA significantly reduced the mass loss rate and heat release rate; addition to the high‐molecular‐weight PMMA provided the largest reductions of these quantities in this study. For fused silica, some reduction in mass loss rate and heat release rate was observed when it was added to the high‐molecular‐weight PMMA; addition to the low‐molecular‐weight PMMA did not reduce either loss rate. Chemical analysis of the collected residues and observation of the sample surface during gasification reveal the accumulation of silica near the surface; the larger its coverage over the sample surface was, less the mass loss rate and heat release rate were. Both the level of accumulation and its surface coverage depended strongly not only on the silica characteristics but also on the melt viscosity of the PMMA. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1541–1553, 2003     

Solitary intraosseous infantile myofibroma of the orbital roof

BACKGROUND: There are several rare tumors that can cause proptosis in an infant, including infantile myofibroma. METHODS: A 3-month-old infant developed a painless, bone-destructive superomedial orbital mass, raising concern for orbital malignant neoplasms. Computed tomography disclosed a bone-destructive mass of the sphenoid wing. On magnetic resonance imaging, the intraosseous mass was well-circumscribed, surrounded by cortical bone, and showed prominent enhancement. RESULTS: Superomedial orbitotomy and biopsy revealed a lesion composed of spindled to stellate cells, without mitotic activity, set in a fibromyxoid stroma. Immunohistochemical stains were positive for vimentin and actin. Ultrastructurally, there were actinlike thin filaments, mitochondria, and rough endoplasmic reticulum confirming a myofibroblastic proliferation and supporting the diagnosis of congenital infantile myofibroma. CONCLUSION: Infantile myofibroma is a benign tumor that occurs rarely in the ocular region but can cause prominent bone destruction, misleading the clinician to suspect a malignant neoplasm.     

Nanoparticle networks reduce the flammability of polymer nanocomposites

Synthetic polymeric materials are rapidly replacing more traditional inorganic materials, such as metals, and natural polymeric materials, such as wood. As these synthetic materials are flammable, they require modifications to decrease their flammability through the addition of flame-retardant compounds. Environmental regulation has restricted the use of some halogenated flame-retardant additives, initiating a search for alternative flame-retardant additives. Nanoparticle fillers are highly attractive for this purpose, because they can simultaneously improve both the physical and flammability properties of the polymer nanocomposite. We show that carbon nanotubes can surpass nanoclays as effective flame-retardant additives if they form a jammed network structure in the polymer matrix, such that the material as a whole behaves rheologically like a gel. We find this kind of network formation for a variety of highly extended carbon-based nanoparticles: single- and multiwalled nanotubes, as well as carbon nanofibres.     

Simplified long-channel MOSFET theory

The now-classic and highly accurate double-integral expression for the drain current flowing in long-channel MOSFET's is shown to be reducible to a completely equivalent single-integral expression. The single-integral expression is used in turn to straightforwardly establish the approximate closed-form results commonly known as the bulk-charge and charge-sheet relationships. Sample computations which illustrate the general utility of the single-integral expression are also presented.     

Application of enhancement mode FET technology for wirelesssubscriber transmit/receive circuits

Single-supply power amplifiers have become the new paradigm in portable phone handsets due to the recent availability of heterojunction bipolar transistor (HBT) and pseudo enhancement mode PHEMT technology. We have developed a true enhancement mode heterostructure insulated-gate FET device (HIGFET) which is suitable for use in both saturated and linear power amplifiers. A three-stage power amplifier designed for 1900-MHz NADC application delivered +30-dBm output power and 41.7% power-added efficiency with an adjacent channel power of -29.8 dBc and alternate adjacent channel power of -48.4 dBc. In addition to this, we have demonstrated excellent noise figure and linearity performance for small-signal applications. At 900 MHz and bias conditions V_DS=1.0 V and I_DSQ=1 mA, a single-stage amplifier achieved a noise figure of 1.17 dB with an associated gain of 18.5 dB. These results make the technology an ideal candidate for application in both transmitter and receiver circuits     

The impact of the Workshop Activity for Gender Equity Simulation in the Academy (WAGES–Academic) in demonstrating cumulative effects of gender bias.

We report experimental evaluation of the Workshop Activity for Gender Equity Simulation in the Academy (WAGES–Academic), a brief, experiential simulation of the cumulative effects of unconscious bias in the academic workplace. We predicted that participants who played WAGES–Academic would demonstrate significantly increased knowledge and retention of gender equity issues in the academic workplace compared with participants in a control condition. Baseline information on general knowledge of workplace gender equity issues was obtained from 1,254 undergraduates. In the second phase, 144 were randomly assigned to complete either WAGES–Academic or a control task, and the immediate effects of the activities were measured. Participants were contacted 7–11 days later to complete an online measure of knowledge retention. Compared with a control condition, WAGES–Academic increased knowledge and retention. This effect occurred irrespective of prior level of sexist beliefs, participant gender, or whether the participant had been on the advantaged or disadvantaged team. Potential use and testing of WAGES–Academic with university faculty and administrators are discussed. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Efficiency of use of metabolizable energy for body weight gain in pasture-based,nonlactating dairy cows

Four cohorts of nonlactating, pregnant dairy cows (n = 50, 47, 45, and 42) were individually fed indoors to determine the amount of feed required for body weight (BW) gain from autumn pasture and commonly used supplementary feeds. These results were used to estimate the apparent efficiency with which metabolizable energy (ME) is used for BW gain (app_k_g). Control cows were offered autumn pasture to estimated maintenance requirements (~0.55 MJ of ME/kg of BW^0.75), with an additional 20 MJ of ME/d allocated for pregnancy and activity. All other cows received the same allowance of autumn pasture and an additional allowance (2.5 or 5.0 kg of dry matter/d) of autumn pasture (Past), spring pasture silage (Psil), maize silage (Msil), cracked maize grain (Mgr), or palm kernel expeller (PKE), resulting in a total of 11 treatments. Individual cow dry matter intake was determined daily; BW was recorded once per week for cohorts 1 and 2, and 3 times per week for cohorts 3 and 4. The ME contents of feeds were estimated from feed quality assays. Regression analyses were used on each feed to determine the ME requirement for 1 kg of BW gain. The app_k_g of Past and Msil was 0.34 and 0.47, respectively; these estimates are in line with published literature. The app_k_g of Psil (0.50) was consistent with the published k_g for spring pasture, from which the silage was made. Palm kernel expeller had the greatest app_k_g (0.61). The reasons for this cannot be deduced from the current study but may reflect the relatively high fat content of the feed and the high k_g of fat. The app_k_g for Mgr was low (0.38) in comparison with the other supplementary feeds and, in particular, relative to its feed ME and published k_g estimates. Although the reason for the low app_k_g cannot be deduced from the current data, the most plausible reason is the preferential use of propionate-derived glucose for conceptus metabolism rather than BW gain, a factor not accounted for in previous experimental models that did not use late-gestation cows. In summary, the app_k_g for autumn pasture was low but consistent with historical growth rate trials in other ruminant species. In comparison, Msil, Psil, and PKE were used with a greater apparent efficiency (app_k_g = 0.47 to 0.61), but Mgr resulted in a relatively low rate of gain per MJ of ME (app_k_g = 0.38). These differences have implications for accurate feed budgeting on farm.     

Narrow emission linewidths of positioned InAs quantum dots grown on pre-patterned GaAs(100) substrates

We report photoluminescence measurements on a single layer of site-controlled InAs quantum dots (QDs) grown by molecular beam epitaxy (MBE) on pre-patterned GaAs(100) substrates with a 15 nm re-growth buffer separating the dots from the re-growth interface. A process for cleaning the re-growth interface allows us to measure single dot emission linewidths of 80 μeV under non-resonant optical excitation, similar to that observed for self-assembled QDs. The dots reveal excitonic transitions confirmed by power dependence and fine structure splitting measurements. The emission wavelengths are stable, which indicates the absence of a fluctuating charge background in the sample and confirms the cleanliness of the re-growth interface.     

Increasing selenium concentration in milk: effects of amount of selenium from yeast and cereal grain supplements

Two experiments were conducted to establish responses in milk Se concentrations in grazing dairy cows to different amounts of dietary Se yeast, and to determine the effects of the Se concentration of the basal diet. The hypothesis tested was that the response in milk, blood, and tissue Se concentrations to supplemental Se would not be affected by whether the Se was from the basal diet or from Se yeast. In addition, by conducting a similar experiment in either early (spring; experiment 1) or late (autumn; experiment 2) lactation, we hypothesized that different Se input-output relationships would result. Both 6-wk experiments involved 60 multiparous Holstein-Friesian cows, all of which had calved in spring. They were allocated to 1 of 10 dietary Se treatments that included 2 types of crushed triticale grain (low Se, approximately 165 μ g of Se/kg of DM; or high Se, approximately 580 μ g/kg of DM) fed at 4 kg of DM/d, and 1 kg of DM/d of pellets formulated to carry 5 quantities of Se yeast (0, 4, 8, 12, or 16 mg of Se). Daily total Se intakes ranged from <2 to >18 mg/cow in both experiments. Milk Se concentrations plateaued after 15 and 7 d of supplementation in experiments 1 and 2, respectively, and then remained at plateau concentrations. Average milk Se concentrations for the plateau period increased as the amount of Se yeast increased, and low- and high-Se grain treatments were different at all quantities of Se yeast, although there was a tendency for this difference to diminish at the greatest concentrations of yeast. There were significant positive, linear relationships between Se intake and the concentrations of Se in milk, which were not affected by the source of Se, and the relationships were similar for both experiments. Therefore, the output of Se in milk in experiment 1 was greater than that in experiment 2 because the milk yield of the cows in early lactation was greater. The estimated proportions of Se partitioned to destinations other than milk and feces increased with the amount of Se in the diet and were greater in experiment 2 than in experiment 1, a result that was supported by Se concentrations in whole blood and plasma and in semitendinosus muscle tissue. If high-Se products are to be produced for human nutrition, it is important to be able to develop feeding systems that produce milk with consistent and predictable Se concentrations so that products can consistently meet specifications. The results indicate that this objective is achievable.     

Amino acid enrichment and compositional changes among mammalian milk proteins and the resulting nutritional consequences

Milk is a hallmark of mammalian evolution: a unique food that has evolved with mammals. Despite the importance of this food, it is not known if variation in AA composition between different species is important to milk proteins or how it might affect the nutritional value of milk. As milk is the only food source for newborn mammals, it has long been speculated that milk proteins should be enriched in essential AA. However, no systematic analysis supports this assumption. Although many factors influence the overall nutritional value of milk, including total protein concentration, we focused here on the AA composition of milk proteins and investigated the possibility that selection drives compositional changes. We identified 9 major milk proteins present in 13 mammalian species and compared them with a large group of nonmilk proteins. Our results indicate heterogeneity in the AA composition of milk proteins, showing significant enrichment and depletion of certain AA in milk-specific proteins. Although high levels of particular AA appear to be consistently maintained, orthologous milk proteins display significant differences in AA composition across species, most notably among the caseins. Interspecies variation of milk composition is thought to be indicative of nutritional optimization to the requirements of the species. In accordance with this, our observations indicate that milk proteins may have adapted to the species-specific nutritional needs of the neonate.